Methane and nitrous oxide fluxes, and carbon dioxide production in boreal forest soil fertilized with wood ash and nitrogen

Abstract

Abstract Wood ash has been used to alleviate nutrient deficiencies and acidification in boreal forest soils. However, ash and nitrogen (N) fertilization may affect microbial processes producing or consuming greenhouse gases: methane (CH 4 ), nitrous oxide (N 2 O) and carbon dioxide (CO 2 ). Ash and N fertilization can stimulate nitrification and denitrification and, therefore, increase N 2 O emission and suppress CH 4 uptake rate. Ash may also stimulate microbial respiration thereby enhancing CO 2 emission. The fluxes of CH 4 , N 2 O and CO 2 were measured in a boreal spruce forest soil treated with wood ash and/or N (ammonium nitrate) during three growing seasons. In addition to in situ measurements, CH 4 oxidation potential, CO 2 production, net nitrification and N 2 O production were studied in laboratory incubations. The mean in situ N 2 O emissions and in situ CO 2 production from the untreated, N, ash and ash + N treatments were not significantly different, ranging from 11 to 17 μ g N 2 O m −2 h −1 and from 533 to 611 mg CO 2 m −2 h −1 . However, ash increased the CH 4 oxidation in a forest soil profile which could be seen both in the laboratory experiments and in the CH 4 uptake rates in situ . The mean in situ CH 4 uptake rate in the untreated, N, ash and ash + N plots were 153 ± 5, 123 ± 8, 188 ± 10 and 178 ± 18 μ g m −2 h −1 , respectively.